The effects of past major climatic fluctuations on the genetic structures of fauna endemic to Namibia’s granite inselbergs

Sara Tromp (2011). The effects of past major climatic fluctuations on the genetic structures of fauna endemic to Namibia’s granite inselbergs PhD Thesis, School of Biological Sciences, The University of Queensland.

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s4003208_Submission_Form.pdf Submission Form application/pdf 197.14KB 3
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Author Sara Tromp
Thesis Title The effects of past major climatic fluctuations on the genetic structures of fauna endemic to Namibia’s granite inselbergs
School, Centre or Institute School of Biological Sciences
Institution The University of Queensland
Publication date 2011-06
Thesis type PhD Thesis
Total pages 163
Total colour pages 9
Total black and white pages 154
Subjects 06 Biological Sciences
Abstract/Summary Past major climatic fluctuations have played a significant role in determining the patterns of genetic variation within and among taxa by causing taxa to experience cycles of population isolation and expansion. Concordance of phylogeographic patterns across taxa has been used to identify general trends in the locations of refugial areas and re-colonisation routes. In the Northern Hemisphere, severe climate cycles resulted in strong concordance of refugial use and hence in genetic patterns, yet in the southern hemisphere and tropical regions, phylogeographic patterns suggest that large-scale migration was unusual and that the majority of biota persisted in multiple localized refugia. Further, although the effects of climate change on taxa associated with montane regions and forested biomes have been well studied, little is known about these effects in arid biomes. My primary research objective was to examine the combined effects of past major climatic fluctuations, geography and species-specific traits on the evolution of taxa endemic to north-western Namibia’s granite inselbergs. To achieve this, I examined a) the phylogenetic relationship of two closely related species of mongoose (Galerella sanguinea and G. nigrata) and b) the phylogeographic structures of four arid-adapted taxa (a mongoose, G. nigrata; a lizard, Agama planiceps; and two rodents, Michalemys namaquensis and Petromyscus shortridgei) in the Namib Desert. Results were interpreted in light of palaeoclimatic, geographic and ecological data. Within this thesis, I examine mitochondrial cytochrome b and nuclear ß-fibrinogen intron 7 sequences providing the first molecular evidence that the black mongoose, G. nigrata, forms a distinct monophyletic clade, separate from its sympatric sister species the slender mongoose, G. sanguinea. Bayesian analyses of cytochrome b sequences estimated that these two species diverged 3.85 – 4.27 million years ago. This divergence time coincided with a glacial maximum during the Plio-Pleistocene that was characterised by a period of strong aridity in southern Africa. Examination of the phenotypic (pelage coloration) and molecular (nuclear and mitochondrial DNA sequences and microsatellite loci) data from 10 additional individuals revealed evidence of potential hybridization between the two species. Thus it appears that the two species have not yet undergone complete reproductive isolation. Secondly, I provide one of the few direct comparisons between the phylogeographic structures of multiple species. I conducted detailed comparative phylogeographic studies of three habitat specialists of differing size, mobility and life history traits (G. nigrata, A. planiceps and P. shortridgei) and a habitat generalist (M. namaquensis) at six study locations across north-western Namibia. Strikingly different phylogeographic patterns were observed in the cytochrome b genealogies of the two rodent species: the habitat specialist, P. shortridgei, showed strong phylogenetic and geographic structure, whilst the generalist, M. namaquensis, lacked any clear geographic structure in the phylogeny. This suggests that habitat preference plays a significant role in determining species’ responses to major climatic events and subsequent changes in their immediate environment. Cytochrome b genealogies also showed clear differences in both the degree and pattern of genetic divergence among the three habitat specialists. In addition, AMOVA and SAMOVA analyses for these species revealed significant genetic differentiation among populations but the inferred barriers to dispersal varied among the species. Major dissimilarities among the phylogeographic patterns of taxa suggest different species-specific responses to climatic fluctuations. This highlights the importance of differences in species’ ecological plasticity, ability to cross geographic barriers and responses to stochastic effects such as environmental change and disease. Given the lack of similar patterns across species we can surmise that there have been no specific habitat refugia in this landscape; rather, inselbergs across the entire study area may have supported populations during some or all of the most recent major climatic fluctuations. Further study of microsatellite data from G. nigrata revealed little significant differentiation among populations and a lack of spatial structure on SAMOVA analysis. These results imply recent migration and possible male-biased dispersal in the black mongoose. This study has several broad implications for the conservation and management of species endemic to north-western Namibia’s granite inselbergs. The final chapter of this thesis highlights the potential negative interplay between anthropogenic activities, such as subsistence farming, mining and poaching, and conservation of this unique ecosystem. Consequently, a set of four key management recommendations has been provided for consideration by Namibia’s Ministry of Environment and Tourism.
Keyword Quaternary
arid biome
Additional Notes Pages to be printed in colour: 1, 25, 28, 30, 81, 113, 114, 143, 163. Pages to be printed landscape: 75, 78, 81, 108-113, 139, 140, 147.

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Created: Wed, 12 Oct 2011, 10:11:47 EST by Miss Sara Tromp on behalf of Library - Information Access Service